This application is based on and claims priority to Japanese Patent Application No. 2000-317137, filed Oct. 17, 2000, the entire contents of which is hereby expressly incorporated by reference.
1. Field of the Invention
The present invention generally relates to an air induction system for an engine, and more particularly relates to an improved air induction system which includes an airflow sensor.
2. Description of Related Art
An internal combustion engine typically has an air induction system including one or more air intake passages that introduces air into one or more combustion chambers of the engine. Typically, each intake passage is provided with a throttle valve that regulates or measures an amount of the air (i.e., controls the airflow rate) passing through the intake passage. The throttle valves are operable by an operator of the engine through an appropriate linkage connecting the throttle valves with an operation device, such as, for example, a throttle lever. The induction system, thus, can deliver a desired amount of air to the combustion chambers.
Such an engine also typically has an ignition system that ignites an air/fuel charge formed in the combustion chambers. A control device such as, for example, an electronic control unit (ECU) is provided to control ignition timing of the ignition system. In some arrangements, the engine can have a fuel injection system that sprays fuel directly or indirectly to the combustion chambers. Injection timing and duration of the fuel injection system also can be controlled by the ECU. Various sensors are provided to sense engine conditions and/or environmental conditions around the engine. These sensors generally send signals to the ECU. The ECU often uses the signals from the sensors to control the ignition system and/or the fuel injection system.
It would be advantageous for the ECU to receive information relating to a current amount of air flowing through the intake passages. Such information can be used in determining desired operating parameters. Usually, a throttle valve position sensor is used for such a purpose. The throttle valve position sensor is coupled with at least one shaft of the throttle valves to sense an angular position of the shaft. The sensor then can send a signal to the ECU. The signal normally is used as a proxy for the current amount of air flow based upon an assumption that the angular position of the throttle valves generally are proportional to the air flow amount. Actually, however, the angular position signal does not completely correspond to the air flow amount because the air flow amount does not necessarily vary linearly relative to the angular position of the throttle valve.
Inaccuracy of the information as to the air flow amount can cause inaccurate control by the ECU and inefficient engine operation. For instance, operating at or near the optimum air/fuel ratio results in greatly reduced emissions. Typically, an amount of fuel is determined to keep the air/fuel ratio in this optimum ratio. The ECU thus controls the injection timing and duration based upon the signal indicating the air amount to determine the air/fuel ratio. If the air amount information is be inaccurate, then the ECU would not be able to accurately calculate a proper fuel injection timing and duration and the air/fuel ratio would deviate from the optimum ratio.
In order to more accurately sense the air amount, an air flow meter can be used. However, currently available flow meters are quite fragile and do not admit to application in rough environmental applications, such as outboard motors. For instance, if the engine is used at sea, salt water can corrode and deteriorate the flow meter. If the engine is used in dusty surroundings, fine particles can also deteriorate the flow meter. In addition, while being used under such conditions, the useful life of the flow meter can be expected to be shortened.
A need therefore exists for an improved air induction system that can protect a flow meter.
In general, limited space may be available for such a protective construction because, in the field of outboard motors, compact construction is a rather significant design parameter. For instance, engines for outboard motors typically are surrounded by a cowling and minimal space is provided for each engine component or device.
Another need thus exists for an improved air induction system that can be compactly constructed will continuing to provide protection to a flow meter.
In accordance with one aspect of the present invention, an internal combustion engine comprises an engine body. A moveable member is moveable relative to the engine body. The engine body and the moveable member together define a combustion chamber. An air induction system is arranged to introduce air into the combustion chamber. The air induction system includes a primary intake passage through which the air flows. A secondary intake passage extends from the primary passage to communicate with the primary passage. At least a portion of the air flows through the secondary passage. A filter is disposed in the secondary passage to filtrate the portion of the air. An airflow sensor is positioned downstream of the filter in the secondary passage to sense a flow amount of the portion of the air.
In accordance with another aspect of the present invention, an internal combustion engine comprises an engine body. A plurality of moveable members are moveable relative to the engine body. The engine body and the moveable members together define a plurality of combustion chambers. An air induction system is arranged to introduce air into the combustion chambers. The air induction system includes a voluminous member defining a plenum chamber. A plurality of intake conduits define at least portions of intake passages connecting the plenum chamber with the combustion chambers. A recessed member is coupled with the voluminous member to define an air passage communicating with the plenum chamber. A filter is disposed within the air passage to divide the air passage into upstream and downstream portions. A flow meter is positioned in the downstream portion to sense a flow amount of the air flowing through the air passage.
In accordance with a further aspect of the present invention, an internal combustion engine comprises an engine body. A moveable member is moveable relative to the engine body. The engine body and the moveable member together define a combustion chamber. An air induction system is arranged to introduce air into the combustion chamber. The air induction system includes an intake conduit through which the air flows. A side conduit extends from the intake conduit. At least a portion of the air flows through the side conduit. A filter is disposed in the side conduit to filtrate the portion of the air. Means are provided for sensing a flow amount of the portion of the air. The sensing means are positioned downstream of the filter in the side conduit.